Device and process for providing moistened breathing gas

ABSTRACT

A respiration moistener ( 1 ) has an inlet ( 3 ), into which incoming gas ( 2 ) to be moistened can be fed. Vapor ( 21 ) is mixed with the incoming gas ( 2 ) in a mixing chamber ( 4 ). Moistened outgoing gas ( 5 ) flows out of an outlet ( 6 ). In cases in which the temperature of the incoming gas ( 2 ) becomes so high that the temperature of the outgoing gas ( 5 ) is above a desired value, the internal desired value is adjusted. The outgoing gas ( 5 ) can then cool to the desired value on its way through the inspiration tube ( 7 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.11/968,316, filed Jan. 2, 2008, that claims the benefit of priorityunder 35 U.S.C. §119 of German Patent Applications DE 10 2007 006 215.1filed Feb. 8, 2007 and DE 10 2007 015 038.7 filed Mar. 29, 2007, theentire contents of each application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention pertains to a device for providing moistenedbreathing gas with a gas inlet, via which moistened incoming gas can befed, and with a gas outlet for the moistened outgoing gas, as well aswith a vapor or moisture feed means, into which a liquid to beevaporated can be fed, and which is provided with an evaporator or anevaporating device, which is controlled by a control device, which setsthe outlet temperature and the outlet moisture of the outgoing gas.

The present invention pertains, furthermore, to a process for providingmoistened breathing gas.

BACKGROUND OF THE INVENTION

Such a device and such a process are known from DE 198 08 590 A1. Theprior-art device is especially a respiration moistener. The prior-artrespiration moistener has a breathing gas line with a gas inlet, intowhich the incoming gas to be moistened can be fed, and a gas outlet,from which the moistened breathing gas is removed. The device has,furthermore, an evaporating device, into which a liquid to be evaporatedcan be fed. The liquid fed is sent by a dispensing pump to anevaporator, which evaporates the liquid to be evaporated and which feedsthe vapor generated into the breathing gas flowing in the breathing gasline. The evaporating device is connected to a control device, whichsets the outlet temperature and the outlet moisture of the breathing gasflowing out of the gas outlet. The outlet temperature and the outletmoisture can be regulated independently from each other. The evaporatingdevice may comprise, for example, a dispensing pump, which delivers aquantity of liquid proportional to the volume flow of the breathing gasthrough the breathing gas line to an evaporating unit. The outlettemperature of the outgoing gas can then be set independently from thefed quantity of liquid by regulating the temperature of the evaporatingunit such that the vapor generated by the evaporator reaches a certaintemperature and a mixture of breathing gas and vapor, which mixture hasthe desired outlet temperature, is obtained.

It should however be borne in mind, in this context, that thetemperature of the vapor cannot be below the boiling point of theliquid. In addition, there are hygienic specifications, which require avapor temperature above the boiling point of the liquid. This may causethe development of an excessively high outlet temperature at the gasoutlet of the device when the inlet temperature assumes excessively highvalues. This may happen, for example, when the breathing gas is fed tothe gas inlet of the respiration moistener by means of a fan or anotherpumping device.

SUMMARY OF THE INVENTION

Based on this state of the art, the basic object of the presentinvention is to provide a device and a process for providing moistenedbreathing gas, which make it possible to feed heated breathing gas.

In the device and the process, the outlet temperature to be expected isdetermined by the control device for a preset desired moisture. In thosecases in which the temperature to be expected is above a predetermineddesired value for the outlet temperature, the outlet temperature is setto a temperature above the desired temperature. Since the breathing gasmust travel over the path through the inspiration tube from the gasoutlet of the device to the so-called Y-piece, the increased outlettemperature at the gas outlet is not harmful, because the outgoing gascan cool on the way from the gas outlet to the Y-piece to the extentthat the desired temperature is again reached at the Y-piece.

The outlet temperature to be expected is preferably determined on thebasis of a measured value for the inlet temperature. Even though it ispossible, in principle, to use empirical values for the inlettemperature, the measurement of the inlet temperature represents anadditional safety feature, because the inlet temperature may vary as afunction of the ambient temperature.

Furthermore, the temperature to be expected is preferably determined asa function of the vapor temperature, which has been set by the controldevice or determined by means of a temperature sensor. The latter offersthe advantage that variations in the vapor temperature can be taken intoaccount.

The determination of a temperature to be expected is based, furthermore,on a minimum allowable vapor temperature. In cases in which the actualvapor temperature is below a minimum allowable vapor temperature, theminimum allowable vapor temperature is therefore used to determine thetemperature to be expected. As a result, it is possible to avoid valuesfor the temperature to be expected that are unacceptable based onhygienic specifications.

To ensure that the temperature of the outgoing gas up to the so-calledY-piece reaches the desired value, the temperature of the outgoing gascan be determined at the proximal end of the inspiration tube by meansof a temperature sensor.

If the temperature of the outgoing gas at the proximal end of theinspiration tube exceeds the preset desired value, the internal desiredvalue, to which the outlet temperature of the outgoing gas is regulated,can be reduced gradually until the temperature of the outgoing gas atthe proximal end of the inspiration tube essentially corresponds to thepredetermined desired value of the outgoing gas.

In addition, it is possible to reduce the amount of heat introduced intothe outgoing gas by gradually reducing the amount of water introducedinto the outgoing gas until the temperature of the outgoing gas at theproximal end of the inspiration tube essentially corresponds to thedesired value of the outgoing gas.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich the preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic respiration moistener according to the invention,in which the output moisture and the outlet temperature can becontrolled either together or separately; and

FIG. 2 is a flow chart showing a process according to the invention forcontrolling the respiration moistener from FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in particular, FIG. 1 shows a moistener 1,with which breathing gas 2 flowing in can be moistened. The breathinggas 2 flowing in enters a mixing chamber 4 via a gas inlet 3. Breathinggas 5 flowing out of the mixing chamber 4 enters an inspiration tube 7via a gas outlet 6. The breathing gas 5 flowing out therefore reaches,via a distal end 8 (spaced a distance from the Y-piece) of theinspiration tube 7, a proximal end 9 (proximate to the Y-piece) of theinspiration tube 7, which tube is connected with its proximal end to aY-piece, not shown in FIG. 1. Finally, completely processed respirationgas 10 enters the patient's airways via the Y-piece from the proximalend 9 of the inspiration tube 7.

A vapor line 11, which leads to an evaporator 12, is connected to themixing chamber 4. A dispensing pump 13, which delivers liquid from aliquid reservoir 14 to the evaporator 12, is arranged upstream of theevaporator 12. The liquid is typically water or anesthetic. Thedispensing pump 13 and the evaporator 12 are connected to a controldevice 15. The control device 15 sets the quantity of liquid fed in andthe temperature of the vapor such that the breathing gas 5 flowing outhas a preset moisture content and a predetermined outlet temperature.Since the inspiration tube 7 is usually heated, the moisture and thetemperature of the breathing gas flowing out can be maintained on theway of the gas through the inspiration tube 7, so that the moisture andthe temperature of the respiration gas 10 at the proximal end 9 of theinspiration tube 7 are equal to the moisture and the temperature of thebreathing gas 5 flowing out.

A vapor temperature sensor 16, which is arranged in the vapor line 11and is connected to the control device 15, is provided for monitoringthe temperature of the vapor generated by the evaporator 12. Anotherinlet temperature sensor 17, which is arranged in the area of the gasinlet 3, is provided for determining the temperature of the breathinggas 2 flowing in. An outlet temperature sensor 18 arranged in the areaof the gas outlet 6 is used to determine the temperature of thebreathing gas 5 flowing out. Finally, the temperature of the respirationgas 10 can be determined with a temperature sensor 19, which is locatedin the area of the proximal end 9 of the inspiration tube 7.

Finally, a flow sensor or flow meter 20 is also provided, whichdetermines the volume flow of the breathing gas flowing in. The flowsensor 20 may likewise be arranged in the area of the gas outlet 6 or atanother suitable point in order to determine the volume flow of thebreathing gas.

The moistener 1 may be operated according to various control concepts. Afirst possibility is to control the moisture and the temperature of thebreathing gas 5 flowing in separately. The dispensing pump 13 is set inthis case by the control device 15 such that a quantity of waterproportional to the volume flow of the breathing gas is delivered to theevaporator 12. The heat output of the evaporator 12 is controlled,furthermore, such that the quantity of water fed will be evaporated andthat vapor with a vapor temperature is generated in the process and ismixed with the breathing gas 2 flowing in, which leads to an outflowingbreathing gas 5 with a predetermined temperature and moisture.

In another control concept, the quantity of water fed to the evaporatorper unit of time is changed corresponding to the deviation of thetemperature of the breathing gas 5 flowing out from a desired value.This control concept requires that the vapor 21 leaving the evaporator12 has a constant vapor temperature. This in turn requires that thetemperature of the evaporator 12 has a small error and that the vapor 21leaving the evaporator 12 assumes the temperature of the evaporator 12.Both conditions are usually met in practice. Changes in the temperatureof the breathing gas 5 flowing out can be corrected in case of thiscontrol concept by changing the quantity of water fed into theevaporator 12 per unit of time.

However, both control concepts reach their limits when the temperatureof the breathing gas 2 flowing in assumes such high values that thedesired value for the temperature of the breathing gas 5 flowing outcannot be complied with any longer, because the temperature of the watervapor 21 cannot be lowered below the boiling point of water in any case.Moreover, hygienic specifications, which require, for example, that thetemperature of the water vapor 21 does not drop below 130° C., must becomplied with in practice as well.

Even though it is also possible, in principle, to reduce the quantity ofwater fed into the evaporator 12 per unit of time and to reduce herebythe quantity of water fed into the breathing gas 2 flowing in, thisleads to a reduction of the moisture in the breathing gas 5 flowing in,so that the lung of the patient being respirated may dry out.

To avoid this risk, the various control concepts are modified accordingto FIG. 2. FIG. 2 shows the essential process steps of a modifiedcontrol process, which may be one of the two control processes asdesired.

The modification of the control process shown in FIG. 2 begins with areading-in step 22, in which various parameters are read in unless theyhad already been read in in preceding process steps not shown in FIG. 2.Specifically, the preset desired value T_(a) _(—) _(set) for thetemperature of the breathing gas 5 flowing out is read in. Otherparameters to be read in are the weight m_(l) of the quantity of liquidfed to the evaporator 12, the weight m_(gd) of the dry breathing gas 2flowing in as well as the weight m_(gl) of the quantity of liquidcontained in the breathing gas 2 flowing in in the vapor form. Thesemeasured variables are likewise determined by suitable measuringsensors. The temperature T_(i) of the breathing gas 2 flowing in is alsoread in from the inlet temperature sensor 17. Furthermore, a heatingtemperature T_(h) is determined, which is basically equal to the heatingtemperature that is necessary for the breathing gas 5 flowing out toassume the desired value T_(a) _(—) _(set), but which is at least equalto the boiling point of the liquid or is the minimum temperaturerequired for hygienic reasons.

A mixing temperature T_(a) _(—) _(calc) to be expected can be calculatedfor the breathing gas 5 flowing out on the basis of these parameters:

$T_{a\_ {calc}} = \frac{{m_{1} \cdot c_{1} \cdot T_{h}} + {m_{gd} \cdot c_{d} \cdot T_{i}} + {m_{gl} \cdot c_{1} \cdot T_{i}}}{{m_{1} \cdot c_{1}} + {m_{gd} \cdot c_{d}} + {m_{gl} \cdot c_{1}}}$

in which c_(l) is the specific heat of the vapor 21 of the liquid andc_(d) is the specific heat of the dry breathing gas 2 flowing in.

The calculation of the mixing temperature T_(a) _(—) _(calc) to beexpected is based on the circumstance that the enthalpy of the breathinggas 5 flowing out is equal, based on the mixing operation, to the sum ofthe enthalpy of the breathing gas 2 flowing in and the enthalpy of thevapor 21 fed in.

The calculation step 23 is followed by a branching step 24, in which itis determined whether the outlet temperature T_(a) _(—) _(calc) to beexpected is greater than the desired value T_(a) _(—) _(set) for thebreathing gas 5 flowing out.

If the temperature T_(a) _(—) _(calc) to be expected is lower than orequal to the preset desired value, the internal desired value is set tothe preset desired value T_(a) _(—) _(set) in an assignment step 25,after which the control process can be continued.

If, by contrast, the temperature T_(a) _(—) _(calc) to be expected isgreater than the preset desired value T_(a) _(—) _(set), the internaldesired value is made equal to the temperature value T_(a) _(—) _(calc)to be expected in an assignment step 26.

If this is so, the temperature T_(a) _(—) _(calc) to be expected of thebreathing gas 5 flowing out is used as the internal desired value forthe control of the temperature of the breathing gas 5 flowing out. Thebreathing gas 5 flowing out of the gas outlet 6 now has a temperaturethat is above the preset desired value T_(a) _(—) _(set). If, bycontrast, the outlet temperature T_(a) _(—) _(calc) to be expected isnot greater than the desired value T_(a) _(—) _(set), the temperature ofthe breathing gas 5 flowing out, which temperature is determined by theoutlet temperature sensor 18, is adjusted to the preset desired valueT_(a) _(—) _(set).

Consequently, the temperature of the breathing gas 5 flowing out may beabove the desired value T_(a) _(—) _(set) if the temperature T of thebreathing gas 2 flowing in assumes excessively high values. However, thebreathing gas 5 flowing out will release heat on its way through theinspiration tube 7 when the heating of the inspiration tube 7 iscontrolled correspondingly. It is therefore possible that thetemperature of the breathing gas 5 flowing out can drop to the desiredvalue T_(a) _(—) _(set) until it reaches the proximal end 9 of theinspiration tube 7.

Furthermore, to monitor the temperature of the respiration gas 10 at theproximal end 9 of the inspiration tube 7, a respiration temperatureT_(y) of the respiration gas 10 is determined by the temperature sensor19. A poll is performed in a branching step 27 following the assignmentstep 26 to determine whether the respiration temperature T_(y)determined is greater than a desired value T_(y) _(—) _(set) of therespiration temperature. If not, the control process is continued.Otherwise, either the quantity of the liquid fed into the evaporator 12is reduced or the temperature of the vapor 21 is lowered in a reducingstep 28 and the control process is subsequently continued.

It shall be noted that the process steps shown in FIG. 2 can be repeatedat periodic intervals.

Regardless of the embodiment of the control process, which is used tocontrol the moisture and the temperature of the outgoing gas, it isadvantageous if the inlet temperature T_(i) of the breathing gas 2flowing in at the gas inlet 3 is known. In addition, the volume flowshould be determined, from which the mass flow can be readily determinedif the pressure is known. In addition, the mass flow can also bedetermined directly by means of a hot wire gas flowmeter or hot film gasflowmeter. In addition, the mass flow of the breathing gas 2 flowing inmay be delivered by a respirator. The mass flow of the liquid fed intothe evaporator 12 is obtained either on the basis of the deliverycapacity of the dispensing pump 13 or from characteristics, which linkthe temperature of the vapor 21 with the temperature of the breathinggas 5 flowing out assuming a certain inlet temperature T_(i).

Furthermore, it shall be noted that it is also possible to use anevaporating device with a capillary pump with integrated evaporator anda downstream heating device instead of the dispensing pump 13 and theevaporator 12. The evaporation takes place in the capillary pump in thiscase. The evaporated quantity of liquid now depends on the evaporationcapacity of the capillary pump. The temperature of the vapor can then bebrought, if desired, to a preset value by the downstream heating device.

The device being described here and the process being described hereoffer a number of advantages. The triggering of a needless alarm isavoided by the device and the process because the moistener 1 continuesto operate even when the temperature of the breathing gas 5 flowing outis above the desired temperature set. On the other hand, the moistener 1can also be operated at high ambient temperatures and moistures. Inparticular, it is possible to feed the breathing gas 2 flowing in bymeans of a blower. Even if only a limited quantity of moisture can befed for physical reasons, excessively dry breathing gas is avoided withthe device because a sufficient amount of moisture is still fed as longas the temperature of the respiration gas 10 at the proximal end 9 doesnot exceed permissible limit values.

According to one variant of the present invention, the vapor feed means11, 12, 13 is designed as a moisture feed means, into which a quantityof liquid that is to be evaporated can be fed and which is provided withan evaporating device, which is controlled by a control device 15, whichsets the outlet temperature and the outlet moisture of the outgoing gas5, the control device 15 determining a temperature of the outgoing gas 5that is to be expected at a given desired moisture and wherein thecontrol device 15 sets the outlet temperature to a temperature above thedesired temperature in cases in which the temperature to be expected isabove a desired value. The control device 15 is connected especially toan inlet temperature sensor 17, with which the inlet temperature of thebreathing gas 2 flowing in can be determined. The breathing gas flow isoptionally determined additionally.

Finally, it shall be pointed out that features and properties which havebeen described in connection with a certain exemplary embodiment canalso be combined with another exemplary embodiment, except when this isruled out for reasons of compatibility.

Finally, it is also pointed out that the singular includes the plural inthe claims and in the specification, except when something else arisesfrom the context. In particular, both the singular and the plural aremeant especially when the indefinite article is used.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

Appendix

List of Reference Numbers 1 Moistener 2 Breathing gas flowing in 3 Gasinlet 4 Mixing chamber 5 Breathing gas flowing out 6 Gas outlet 7Inspiration tube 8 Distal end 9 Proximal end 10 Respiration gas 11 Vaporline 12 Evaporator 13 Dispensing pump 14 Liquid reservoir 15 Controldevice 16 Vapor temperature sensor 17 Inlet temperature sensor 18 Outlettemperature sensor 19 Temperature sensor 20 Flow sensor 21 Vapor 22Reading-in step 23 Calculation step 24 Branching step 25 Assignment step26 Assignment step 27 Branching step 28 Reducing step

What is claimed is:
 1. A process for providing moistened breathing gas, the process comprising the steps of: feeding incoming gas to be moistened into a gas inlet of a moistener; feeding of liquid into a vapor feed device of the moistener; evaporating the fed liquid by means of an evaporating device; mixing the incoming gas with the vapor to form a moistened outgoing gas; removing the moistened breathing gas from a gas outlet of the moistener; setting the outlet temperature and the outlet moisture of the outgoing gas by means of a control device connected to the evaporating device, wherein an outlet temperature that is to be expected is determined by the control device for a preset desired moisture of the outgoing gas, and the outlet temperature of the outgoing gas is set by the control device to a temperature above the desired value in cases in which the outlet temperature to be expected exceeds a desired value.
 2. A process in accordance with claim 1, wherein the inlet temperature of the incoming gas is determined by the control device.
 3. A process in accordance with claim 1, wherein the temperature of the vapor generated by the evaporating device is set by the control device.
 4. A process in accordance with claim 1, wherein the temperature of the outgoing gas that is to be expected is calculated by taking into account a minimum allowable temperature of the vapor generated by the evaporating device.
 5. A process in accordance with claim 1, wherein the temperature of the outgoing gas is adjusted to the temperature to be expected.
 6. A process in accordance with claim 1, wherein the breathing gas temperature is determined in the area of a proximal end of a line connected to the gas outlet by means of a temperature sensor.
 7. A process in accordance with claim 6, wherein the temperature of the vapor generated by the evaporating device is reduced when the breathing gas temperature is above a preset limit value.
 8. A process in accordance with claim 6, wherein the quantity of liquid evaporated in the evaporating device is reduced when the breathing gas temperature exceeds a preset limit value.
 9. A process in accordance with claim 7, wherein the reduction operations are carried out gradually.
 10. A process for providing moistened breathing gas, the process comprising the steps of: providing a mixing chamber; providing a gas inlet; feeding incoming gas, that is to be moistened, through the gas inlet to the mixing chamber; providing a gas outlet; providing a moisture feed means including a dispensing pump feeding a quantity of liquid that is to be evaporated to an evaporating device; evaporating the fed liquid in the evaporating device to feed vapor with a vapor temperature to the mixing chamber; supplying moistened outgoing gas from the mixing chamber via the gas outlet; providing a control device; controlling, with the control device, the quantity of liquid fed to the evaporating device by the dispensing pump; controlling, with the control device, a heat output of the evaporating device such that the quantity of liquid fed will be evaporated and such that the vapor with the vapor temperature is generated at the evaporating device and is fed to the mixing chamber; setting an outlet desired temperature and an outlet moisture level of the outgoing gas, with the control device; determining a temperature of the outgoing gas that is to be expected at a given desired moisture, with the control device; setting an outlet temperature of the outgoing gas to a temperature above the desired temperature when the temperature to be expected of the outgoing gas, at the set moisture level, is above the desired temperature.
 11. A process in accordance with claim 10, further comprising the steps of: providing an inlet temperature sensor connected to the control device; determining, with the inlet temperature sensor, the inlet temperature of the breathing gas flowing in.
 12. A process in accordance with claim 10, further comprising the steps of: providing an inspiration tube connected to the gas outlet; and providing a patient proximal temperature sensor at a patient proximal end of the inspiration tube, the control device being connected to the patient proximal temperature sensor; determining a breathing gas temperature, with the patient proximal temperature sensor, of respiration gas which flows out of the patient proximal end of the inspiration tube.
 13. A process in accordance with claim 12, further comprising the step of: reducing, with the control device, the temperature of the vapor generated by the evaporating device when the breathing gas temperature determined at the end of the inspiration tube exceeds a predetermined limit value.
 14. A process in accordance with claim 13, further comprising the step of: reducing, with the control device, the quantity of liquid fed to the evaporating device when the breathing gas temperature determined at the end of the inspiration tube exceeds a predetermined limit value.
 15. A process in accordance with claim 12, wherein: the control device receives parameters for operation including the desired temperature of the outgoing gas; upon the control device determining the temperature of the outgoing gas that is to be expected, at the given desired moisture, is above the desired temperature, the control device sets the desired temperature to the temperature of the outgoing gas that is to be expected; upon the control device setting the desired temperature to the temperature of the outgoing gas that is to be expected the control device determines if the breathing gas temperature determined at the end of the inspiration tube exceeds a predetermined limit value; and upon the control device determining that the breathing gas temperature at the end of the inspiration tube exceeds a predetermined limit value, the control device reduces one of: the temperature of the vapor generated by the evaporating device; and the quantity of liquid fed to the evaporating device. 